Read any game or series preview and most of the focus will be on the teams and the players. As it ought to be, as games and series are competitions between teams made up of players. What we always want to believe is that the team with the players who perform better will emerge triumphant. But of course, what we know is that there are not countless variables, but there are more variables than we would like to count. It matters what the environment is. It matters what the weather is. It matters what other things are. And it matters who the home-plate umpire is. Because home-plate umpires are human, not all home-plate umpires are identical, so not all home-plate umpires will have the same effect on any given game.

It’s worthwhile, then, to talk a little bit about the home-plate umpire in anticipation of the start of the World Series. For tonight’s Game 1, the crew chief and guy behind the plate will be Gerry Davis. You might remember Gerry Davis for drawing some strike-zone criticism in last year’s playoffs, from the Yankees. You might alternately remember Gerry Davis for just being an umpire you’ve heard of, or for being a guy who lives on your block if you live near him. For the remainder of this post, we’re going to examine Gerry Davis’ average strike zone. For Justin Verlander, Barry Zito, and many of the rest of the Tigers and Giants, this is going to be some sort of factor.

We turn to BaseballHeatMaps.com. Since 2008 — during the PITCHf/x Era — Davis has been behind the plate for nearly 3,000 innings. PITCHf/x has captured most of the pitches thrown during those innings, and many of those pitches were taken for balls or strikes. What follows are two heat maps, showing Davis’ 2008-2012 strike zones compared to the league-average strike zones. We’re breaking things up by lefty batters and righty batters, as we ought to.

Right-handed batters

All that blue means fewer strikes, which means more hitter-friendly. This is from the catcher’s perspective, so the left side is inside and the right side is outside. Over the past five years, Davis has been stingy with the inner and outer edges. Otherwise he’s been more or less normal, but immediately we can tell that Davis has one of baseball’s smaller strike zones.

Left-handed batters

Again, we see lots of blue without any yellow or red. Davis really hasn’t liked calling the inside strike against lefty hitters. He’ll grant the outside strike, but to a lesser degree than the average, although the sample size out there is going to be limited. Again, we can conclude that Davis has a smaller strike zone, and it doesn’t require much of a leap to suggest that’s worse news for Barry Zito than it is for Justin Verlander. Verlander has sufficiently good stuff to survive coming over the middle. Zito would very much prefer to not have to do that.

In Zito, you’ve got a guy who’d probably like to live on or near the edges. Davis might be less granting of those edges, meaning Zito in theory would have to either get more of the plate or risk walk trouble. I don’t know which would be better or worse, to be honest. A smaller strike zone wouldn’t do Verlander any favors, of course, since he’s a pitcher, but it goes without saying that he’s hard to hit no matter where he throws the baseball.

To keep digging, Davis last umped for Verlander on May 24, 2011. In that game Verlander allowed six runs in six innings, with zero walks and two strikeouts. Davis last umped for Zito on April 25, 2012. In that game Zito allowed one run in six innings, with two walks and four strikeouts. I regret introducing this information because somebody out there is going to make too much of it. Still, let’s show some .gifs of Davis making decisions on Verlander and Zito pitches. All of these pitches were borderline pitches.

It’s important to understand that just because Davis has his average strike zones doesn’t mean he always calls according to those strike zones. He’s human, again, and humans are often wildly inconsistent. In some of those .gifs above, you can see Davis granting strikes on balls, and he’s also called balls on strikes. Everything is judged on a case-by-case basis so we can’t just declare that Davis will have a small zone on Wednesday. I’d say he’s just more likely to have a small zone than many other would-be umpires. I suspect Zito will find out about Davis’ Game 1 strike zone pretty quick. Nearly all of Zito’s pitches will be thrown to right-handed batters.

Finally, for whatever this might be worth: since 2008, Davis’ ERA has dropped from 4.64 to 3.90, while the league ERA has dropped from 4.32 to 4.01. Meanwhile, Davis’ strikeout-to-walk ratio has climbed from 1.9 to 2.6, while the league strikeout-to-walk ratio has climbed from 2.0 to 2.5. In each season, Davis has umped around 600 innings. It’s possible that Davis has become more pitcher-friendly over time. It’s possible his strike zone now isn’t as small as it used to be. I can’t think of any research that’s been done on umpiring trends, and I can’t think of reasons why Davis would change, but the numbers are the numbers and the sample sizes aren’t that tiny. Maybe Zito will end up getting some generous calls.

Or maybe he won’t, and maybe that’ll be the whole reason that Zito gets absolutely blasted. Gerry Davis is just another variable, and like with almost all the other variables, he’s tricky to predict.